How to extract a String from a changing template in Java?

Question

I have a question regarding best practices considering Java regular expressions/Strings manipulation.

I have a changing String template, let's say this time it looks like this:

 /get/{id}/person

I have another String that matches this pattern eg.

/get/1234ewq/person

Keep in mind that the pattern could change anytime, slashes could disappear etc.

I would like to extract the difference between the two of them i.e. the result of the processing would be 1234ewq. I know I could iterate over them char by char and compare, but, if it is possible, I wanted to find some smart approach to it with regular expressions.

What would be the best Java approach? Thank you.

So essentially you want to get the difference between two strings? Are the start and the end of both strings always the same? — Uli Sotschok, Mar 06 '19 at 20:30
they have parts that are the same, but they do not have to be at beginning or the end — KompiKompi, Mar 06 '19 at 20:34
The following question could be related to yours: [Extract the difference between two strings in Java](https://stackoverflow.com/q/18344721/8411228) — Uli Sotschok, Mar 06 '19 at 20:40
@KompiKompi, could you give me some feedback as to whether my answer helped you or are there any other points that still need to be clarified? — FlorianDe, Mar 18 '19 at 20:32
your answer is ok, although I ended up using a different approach — KompiKompi, Mar 20 '19 at 10:26

FlorianDe · Answer 1 · 2019-03-06T23:08:11.920

For you to answer your question with a regex approach I built a small example class which should hint you into a direction you could go with this (see below).

The problem with this approach is that you dynamically create a regular expression that depends on your template strings. This means that you have to somehow verify that your templates do not interfere with the regex compilation and matching process itself. Also atm if you would use the same placeholder multiple times within a template the resulting HashMap only contains the value for the last placeholder mapping of that kind. Normally this is the expected behaviour but this depends on your strategy of filling your templates.

For template processing in general you could have a look at the mustache library. Also as Uli Sotschok mentioned, you probably would be better of with using something like google-diff-match-patch.

public class StringExtractionFromTemplate {
    public static void main(String[] args) {
        String template =  "/get/{id}/person";
        String filledTemplate = "/get/1234ewq/person";

        System.out.println(diffTemplateInsertion(template, filledTemplate).get("id"));
    }


    private static HashMap<String, String> diffTemplateInsertion(String template, String filledTemplate){
        //language=RegExp
        String placeHolderPattern = "\\{(.+)}";

        HashMap<String, String> templateTranslation = new HashMap<>();

        String regexedTemplate = template.replaceAll(placeHolderPattern, "(.+)");
        Pattern pattern = Pattern.compile(regexedTemplate);

        Matcher templateMatcher = pattern.matcher(template);
        Matcher filledTemplateMatcher = pattern.matcher(filledTemplate);

        while (templateMatcher.find() && filledTemplateMatcher.find()) {
            if(templateMatcher.groupCount() == filledTemplateMatcher.groupCount()){
                for (int i = 1; i <= templateMatcher.groupCount(); i++) {
                    templateTranslation.put(
                            templateMatcher.group(i).replaceAll(placeHolderPattern,"$1"), 
                            filledTemplateMatcher.group(i)
                    );
                }
            }
        }

        return templateTranslation;
    }
}

How to extract a String from a changing template in Java?

1 Answers1